User Equipment with Selective Neighbor Cell Detection

ABSTRACT

Performing selective tune-away by a user equipment (UE). The UE may include a first radio that is configurable to operate according to a first radio access technology (RAT) and a second RAT. The UE may use the radio to communicate using the first RAT and the second RAT using the first radio. The UE may also perform measurement of a received signal strength for the first RAT. The UE may determine if the received signal strength is less than a threshold. Neighbor cell measurement and/or synchronization may be performed if the received signal strength is less than the threshold. However, if the received signal strength is greater than the threshold, the neighbor cell measurement and/or synchronization may not be performed. The UE may continue to perform page decoding for the first RAT using the first radio, e.g., for each discontinuous reception (DRX) cycle of the first RAT.

PRIORITY INFORMATION

The present application claims benefit of priority of U.S. ProvisionalApplication Ser. No. 61/948,280, titled “User Equipment with ImprovedTune-Away Performance”, whose inventors are Li Su, Wanping Zhang,Yingjie Zhao, and Yulin Wang, which was filed on Mar. 5, 2014, and whichis hereby incorporated by reference in its entirety as though fully andcompletely set forth herein.

FIELD OF THE INVENTION

The present application relates to wireless devices, and moreparticularly to a system and method for providing improved performanceand/or reduced power consumption in wireless devices that supportmultiple radio access technologies (RATs).

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. Further,wireless communication technology has evolved from voice-onlycommunications to also include the transmission of data, such asInternet and multimedia content. Therefore, improvements are desired inwireless communication. In particular, the large amount of functionalitypresent in a user equipment (UE), e.g., a wireless device such as acellular phone, can place a significant strain on the battery life ofthe UE. Further, where a UE is configured to support multiple radioaccess technologies (RATs), certain performance degradations can occuron one or more of the RATs, such as due to tune-away operations of theother RAT. As a result, techniques are desired which provide powersavings and/or improved performance in such wireless UE devices.

New and improved cellular radio access technologies (RATs) are sometimesdeployed in addition to existing RATs. For example, networksimplementing Long Term Evolution (LTE) technology, developed andstandardized by the Third Generation Partnership Project (3GPP), arecurrently being deployed. LTE and other newer RATs often support fasterdata rates than networks utilizing legacy RATs, such as various secondgeneration (2G) and third generation (3G) RATs.

However, in some deployments, LTE and other new RATs may not fullysupport some services that can be handled by legacy networks.Accordingly, LTE networks are often co-deployed in overlapping regionswith legacy networks and UE devices may transition between RATs asservices or coverage may require. For example, in some deployments, LTEnetworks are not capable of supporting voice calls. Thus, for examplewhen a UE device receives or initiates a circuit switched voice callwhile connected to an LTE network that does not support voice calls, theUE device can transition to a legacy network, such as one which uses aGSM (Global System for Mobile Communications) RAT or a “1X” (CodeDivision Multiple Access 2000 (CDMA2000) 1X) RAT that supports voicecalls, among other possibilities.

Some UE devices use a single radio to support operation on multiplecellular RATs. For example, some UE devices use a single radio tosupport operation on both LTE and GSM networks. The use of a singleradio for multiple RATs makes transitioning between networks, such as inresponse to a page message for an incoming voice call or circuitswitched service, more complex. In addition, the use of a single radiofor multiple RATs presents certain power usage and performance issues.

For example, in such systems the UE may periodically tune from the firstnetwork, using a more advanced RAT, to the second network, using alegacy RAT, e.g., to listen to a paging channel for a voice call.However, such tune-away operations from a more advanced RAT, such asLTE, to a legacy RAT, such as GSM, can result in increased powerconsumption and/or performance degradation of the LTE network.

Therefore, it would be desirable to provide improved performance andpower consumption in wireless communication systems where a UE devicesuse a single radio to support operation on multiple cellular RATs.

SUMMARY OF THE INVENTION

Embodiments described herein relate to a User Equipment (UE) device andassociated method for performing selective tune-away. The UE may includea first radio that is configurable to operate according to a first radioaccess technology (RAT) and a second RAT. The UE may use the radio tocommunicate using the first RAT and the second RAT using the firstradio. The UE may also perform measurement of a received signal strengthfor the second RAT. The UE may determine if the received signal strengthis less than a threshold. Neighbor cell measurement and/orsynchronization may be performed if the received signal strength is lessthan the threshold. However, if the received signal strength is greaterthan the threshold, the neighbor cell measurement and/or synchronizationmay not be performed. The UE may continue to perform page decoding forthe second RAT using the first radio, e.g., for each discontinuousreception (DRX) cycle of the second RAT.

Embodiments described herein relate to a User Equipment (UE) device andassociated method for performing handover in a UE. The UE may include asingle radio that is configured for communication using a first radioaccess technology (RAT) and a second RAT. The UE may perform handoverfrom a first base station to a second base station on a first radioaccess technology (RAT) during a first handover period using the singleradio. During the first handover period, the UE may perform pagedecoding for the second RAT using the single radio. However, during thefirst handover period, the UE may not perform a neighbor cellsynchronization for reselection of the second RAT. After the firsthandover period, UE may perform neighbor cell synchronization forreselection of the second RAT using the single radio.

This Summary is provided for purposes of summarizing some exemplaryembodiments to provide a basic understanding of aspects of the subjectmatter described herein. Accordingly, the above-described features aremerely examples and should not be construed to narrow the scope orspirit of the subject matter described herein in any way. Otherfeatures, aspects, and advantages of the subject matter described hereinwill become apparent from the following Detailed Description, Figures,and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the embodiments is considered inconjunction with the following drawings.

FIG. 1 illustrates an example user equipment (UE) according to oneembodiment;

FIG. 2 illustrates an example wireless communication system where a UEcommunicates with two base stations using two different RATs;

FIG. 3 is an example block diagram of a base station, according to oneembodiment;

FIG. 4 is an example block diagram of a UE, according to one embodiment;

FIGS. 5A and 5B are example block diagrams of wireless communicationcircuitry in the UE, according to one embodiment;

FIG. 6 is a flowchart diagram illustrating an exemplary method forperforming measurement and/or synchronization;

FIG. 7 is a flowchart diagram illustrating an exemplary method forperforming page decoding during handover; and

FIG. 8 is an exemplary timing diagram corresponding to one embodiment ofFIG. 7.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS Acronyms

The following acronyms are used in the present disclosure.

-   -   3GPP: Third Generation Partnership Project    -   3GPP2: Third Generation Partnership Project 2    -   GSM: Global System for Mobile Communications    -   UMTS: Universal Mobile Telecommunications System    -   LTE: Long Term Evolution    -   RAT: Radio Access Technology    -   TX: Transmit    -   RX: Receive

Terms

The following is a glossary of terms used in the present application:

Memory Medium—Any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a CD-ROM, floppy disks, or tape device; a computer system memoryor random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, RambusRAM, etc.; a nonvolatile memory such as a Flash, magnetic media, e.g., ahard drive, or optical storage; registers, or other similar types ofmemory elements, etc. The memory medium may include other types ofmemory as well or combinations thereof. In addition, the memory mediummay be located in a first computer system in which the programs areexecuted, or may be located in a second different computer system whichconnects to the first computer system over a network, such as theInternet. In the latter instance, the second computer system may provideprogram instructions to the first computer for execution. The term“memory medium” may include two or more memory mediums which may residein different locations, e.g., in different computer systems that areconnected over a network. The memory medium may store programinstructions (e.g., embodied as computer programs) that may be executedby one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), personal communication device, smart phone, televisionsystem, grid computing system, or other device or combinations ofdevices. In general, the term “computer system” can be broadly definedto encompass any device (or combination of devices) having at least oneprocessor that executes instructions from a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™, PlayStation Portable™, Gameboy Advance™,iPhone™), laptops, PDAs, portable Internet devices, music players, datastorage devices, other handheld devices, as well as wearable devicessuch as wrist-watches, headphones, pendants, earpieces, etc. In general,the term “UE” or “UE device” can be broadly defined to encompass anyelectronic, computing, and/or telecommunications device (or combinationof devices) which is easily transported by a user and capable ofwireless communication.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Processing Element—refers to various elements or combinations ofelements. Processing elements include, for example, circuits such as anASIC (Application Specific Integrated Circuit), portions or circuits ofindividual processor cores, entire processor cores, individualprocessors, programmable hardware devices such as a field programmablegate array (FPGA), and/or larger portions of systems that includemultiple processors.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIG. 1—User Equipment

FIG. 1 illustrates an example user equipment (UE) 106 according to oneembodiment. The term UE 106 may be any of various devices as definedabove. UE device 106 may include a housing 12 which may be constructedfrom any of various materials. UE 106 may have a display 14, which maybe a touch screen that incorporates capacitive touch electrodes. Display14 may be based on any of various display technologies. The housing 12of the UE 106 may contain or comprise openings for any of variouselements, such as home button 16, speaker port 18, and other elements(not shown), such as microphone, data port, and possibly various othertypes of buttons, e.g., volume buttons, ringer button, etc.

The UE 106 may support multiple radio access technologies (RATs). Forexample, UE 106 may be configured to communicate using any of variousRATs such as two or more of Global System for Mobile Communications(GSM), Universal Mobile Telecommunications System (UMTS), Code DivisionMultiple Access (CDMA) (e.g., CDMA2000 1XRTT or other CDMA radio accesstechnologies), Long Term Evolution (LTE), Advanced LTE, and/or otherRATs. For example, the UE 106 may support at least two radio accesstechnologies such as LTE and GSM. Various different or other RATs may besupported as desired.

The UE 106 may comprise one or more antennas. The UE 106 may alsocomprise any of various radio configurations, such as variouscombinations of one or more transmitter chains (TX chains) and one ormore receiver chains (RX chains). For example, the UE 106 may comprise aradio that supports two or more RATs. The radio may comprise a single TX(transmit) chain and a single RX (receive) chain. Alternatively, theradio may comprise a single TX chain and two RX chains that operate onthe same frequency. In another embodiment, the UE 106 comprises two ormore radios, i.e., two or more TX/RX chains (two or more TX chains andtwo or more RX chains).

In the embodiment described herein, the UE 106 comprises two antennaswhich communicate using two or more RATs. For example, the UE 106 mayhave a pair of cellular telephone antennas coupled to a single radio orshared radio. The antennas may be coupled to the shared radio (sharedwireless communication circuitry) using switching circuits and otherradio-frequency front-end circuitry. For example, the UE 106 may have afirst antenna that is coupled to a transceiver or radio, i.e., a firstantenna that is coupled to a transmitter chain (TX chain) fortransmission and which is coupled to a first receiver chain (RX chain)for receiving. The UE 106 may also comprise a second antenna that iscoupled to a second RX chain. The first and second receiver chains mayshare a common local oscillator, which means that both of the first andsecond receiver chains tune to the same frequency. The first and secondreceiver chains may be referred to as the primary receiver chain (PRX)and the diversity receiver chain (DRX).

In one embodiment, the PRX and DRX receiver chains operate as a pair andtime multiplex among two or more RATs, such as LTE and one or more otherRATs such as GSM or CDMA1x. In the primary embodiment described hereinthe UE 106 comprises one transmitter chain and two receiver chains (PRXand DRX), wherein the transmitter chain and the two receiver chains(acting as a pair) time multiplex between two (or more) RATs, such asLTE and GSM.

Each antenna may receive a wide range of frequencies such as from 600MHz up to 3 GHz. Thus, for example, the local oscillator of the PRX andDRX receiver chains may tune to a specific frequency such as an LTEfrequency band, where the PRX receiver chain receives samples fromantenna 1 and the DRX receiver chain receives samples from antenna 2,both on the same frequency (since they use the same local oscillator).The wireless circuitry in the UE 106 can be configured in real timedepending on the desired mode of operation for the UE 106. In theexample embodiment described herein, the UE 106 is configured to supportLTE and GSM radio access technologies.

FIG. 2—Communication System

FIG. 2 illustrates an exemplary (and simplified) wireless communicationsystem. It is noted that the system of FIG. 2 is merely one example of apossible system, and embodiments may be implemented in any of varioussystems, as desired.

As shown, the exemplary wireless communication system includes basestations 102A and 102B which communicate over a transmission medium withone or more user equipment (UE) devices, represented as UE 106. The basestations 102 may be base transceiver stations (BTS) or cell sites, andmay include hardware that enables wireless communication with the UE106. Each base station 102 may also be equipped to communicate with acore network 100. For example, base station 102A may be coupled to corenetwork 100A, while base station 102B may be coupled to core network100B. Each core network may be operated by a respective cellular serviceprovider, or the plurality of core networks 100A may be operated by thesame cellular service provider. Each core network 100 may also becoupled to one or more external networks (such as external network 108),which may include the Internet, a Public Switched Telephone Network(PSTN), and/or any other network. Thus, the base stations 102 mayfacilitate communication between the UE devices 106 and/or between theUE devices 106 and the networks 100A, 100B, and 108.

The base stations 102 and the UEs 106 may be configured to communicateover the transmission medium using any of various radio accesstechnologies (“RATs”, also referred to as wireless communicationtechnologies or telecommunication standards), such as GSM, UMTS (WCDMA),LTE, LTE Advanced (LTE-A), 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD,eHRPD), IEEE 802.11 (WLAN or Wi-Fi), IEEE 802.16 (WiMAX), etc.

Base station 102A and core network 100A may operate according to a firstRAT (e.g., LTE) while base station 102B and core network 100B mayoperate according to a second (e.g., different) RAT (e.g., GSM, CDMA2000 or other legacy or circuit switched technologies). The two networksmay be controlled by the same network operator (e.g., cellular serviceprovider or “carrier”), or by different network operators, as desired.In addition, the two networks may be operated independently of oneanother (e.g., if they operate according to different RATs), or may beoperated in a somewhat coupled or tightly coupled manner.

Note also that while two different networks may be used to support twodifferent RATs, such as illustrated in the exemplary networkconfiguration shown in FIG. 2, other network configurations implementingmultiple RATs are also possible. As one example, base stations 102A and102B might operate according to different RATs but couple to the samecore network. As another example, multi-mode base stations capable ofsimultaneously supporting different RATs (e.g., LTE and GSM, LTE andCDMA2000 1xRTT, and/or any other combination of RATs) might be coupledto a core network that also supports the different cellularcommunication technologies. In one embodiment, the UE 106 may beconfigured to use a first RAT that is a packet-switched technology(e.g., LTE) and a second RAT that is a circuit-switched technology(e.g., GSM or 1xRTT).

As discussed above, UE 106 may be capable of communicating usingmultiple RATs, such as those within 3GPP, 3GPP2, or any desired cellularstandards. The UE 106 might also be configured to communicate usingWLAN, Bluetooth, one or more global navigational satellite systems(GNSS, e.g., GPS or GLONASS), one and/or more mobile televisionbroadcasting standards (e.g., ATSC-M/H or DVB-H), etc. Othercombinations of network communication standards are also possible.

Base stations 102A and 102B and other base stations operating accordingto the same or different RATs or cellular communication standards maythus be provided as a network of cells, which may provide continuous ornearly continuous overlapping service to UE 106 and similar devices overa wide geographic area via one or more radio access technologies (RATs).

FIG. 3—Base Station

FIG. 3 illustrates an exemplary block diagram of a base station 102. Itis noted that the base station of FIG. 3 is merely one example of apossible base station. As shown, the base station 102 may includeprocessor(s) 504 which may execute program instructions for the basestation 102. The processor(s) 504 may also be coupled to memorymanagement unit (MMU) 540, which may be configured to receive addressesfrom the processor(s) 504 and translate those addresses to locations inmemory (e.g., memory 560 and read only memory (ROM) 550) or to othercircuits or devices.

The base station 102 may include at least one network port 570. Thenetwork port 570 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above.

The network port 570 (or an additional network port) may also oralternatively be configured to couple to a cellular network, e.g., acore network of a cellular service provider. The core network mayprovide mobility related services and/or other services to a pluralityof devices, such as UE devices 106. In some cases, the network port 570may couple to a telephone network via the core network, and/or the corenetwork may provide a telephone network (e.g., among other UE devices106 serviced by the cellular service provider).

The base station 102 may include at least one antenna 534. The at leastone antenna 534 may be configured to operate as a wireless transceiverand may be further configured to communicate with UE devices 106 viaradio 530. The antenna 534 communicates with the radio 530 viacommunication chain 532. Communication chain 532 may be a receive chain,a transmit chain or both. The radio 530 may be configured to communicatevia various RATs, including, but not limited to, LTE, GSM, WCDMA,CDMA2000, etc.

The processor(s) 504 of the base station 102 may be configured toimplement part or all of the methods described herein, e.g., byexecuting program instructions stored on a memory medium (e.g., anon-transitory computer-readable memory medium). Alternatively, theprocessor 504 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (ApplicationSpecific Integrated Circuit), or a combination thereof.

FIG. 4—User Equipment (UE)

FIG. 4 illustrates an example simplified block diagram of a UE 106. Asshown, the UE 106 may include a system on chip (SOC) 400, which mayinclude portions for various purposes. The SOC 400 may be coupled tovarious other circuits of the UE 106. For example, the UE 106 mayinclude various types of memory (e.g., including NAND flash 410), aconnector interface 420 (e.g., for coupling to a computer system, dock,charging station, etc.), the display 460, cellular communicationcircuitry 430 such as for LTE, GSM, etc., and short range wirelesscommunication circuitry 429 (e.g., Buletooth and WLAN circuitry). The UE106 may further comprise one or more smart cards 310 that comprise SIM(Subscriber Identity Module) functionality, such as one or more UICC(s)(Universal Integrated Circuit Card(s)) cards 310. The cellularcommunication circuitry 430 may couple to one or more antennas,preferably two antennas 435 and 436 as shown. The short range wirelesscommunication circuitry 429 may also couple to one or both of theantennas 435 and 436 (this connectivity is not shown for ease ofillustration).

As shown, the SOC 400 may include processor(s) 402 which may executeprogram instructions for the UE 106 and display circuitry 404 which mayperform graphics processing and provide display signals to the display460. The processor(s) 402 may also be coupled to memory management unit(MMU) 440, which may be configured to receive addresses from theprocessor(s) 402 and translate those addresses to locations in memory(e.g., memory 406, read only memory (ROM) 450, NAND flash memory 410)and/or to other circuits or devices, such as the display circuitry 404,cellular communication circuitry 430, short range wireless communicationcircuitry 429, connector I/F 420, and/or display 460. The MMU 440 may beconfigured to perform memory protection and page table translation orset up. In some embodiments, the MMU 440 may be included as a portion ofthe processor(s) 402.

In one embodiment, as noted above, the UE 106 comprises at least onesmart card 310, such as a UICC 310, which executes one or moreSubscriber Identity Module (SIM) applications and/or otherwise implementSIM functionality. The at least one smart card 310 may be only a singlesmart card 310, or the UE 106 may comprise two or more smart cards 310.Each smart card 310 may be embedded, e.g., may be soldered onto acircuit board in the UE 106, or each smart card 310 may be implementedas a removable smart card. Thus the smart card(s) 310 may be one or moreremovable smart cards (such as UICC cards, which are sometimes referredto as “SIM cards”), and/or the smart card(s) 310 may be one or moreembedded cards (such as embedded UICCs (eUICCs), which are sometimesreferred to as “eSIMs” or “eSIM cards”). In some embodiments (such aswhen the smart card(s) 310 include an eUICC), one or more of the smartcard(s) 310 may implement embedded SIM (eSIM) functionality; in such anembodiment, a single one of the smart card(s) 310 may execute multipleSIM applications. Each of the smart card(s) 310 may include componentssuch as a processor and a memory; instructions for performing SIM/eSIMfunctionality may be stored in the memory and executed by the processor.In one embodiment, the UE 106 may comprise a combination of removablesmart cards and fixed/non-removable smart cards (such as one or moreeUICC cards that implement eSIM functionality), as desired. For example,the UE 106 may comprise two embedded smart cards 310, two removablesmart cards 310, or a combination of one embedded smart card 310 and oneremovable smart card 310. Various other SIM configurations are alsocontemplated.

As noted above, in one embodiment, the UE 106 comprises two or moresmart cards 310, each implementing SIM functionality. The inclusion oftwo or more SIM smart cards 310 in the UE 106 may allow the UE 106 tosupport two different telephone numbers and may allow the UE 106 tocommunicate on corresponding two or more respective networks. Forexample, a first smart card 310 may comprise SIM functionality tosupport a first RAT such as LTE, and a second smart card 310 maycomprise SIM functionality to support a second RAT such as GSM. Otherimplementations and RATs are of course possible. Where the UE 106comprises two smart cards 310, the UE 106 may support Dual SIM DualActive (DSDA) functionality. The DSDA functionality may allow the UE 106to be simultaneously connected to two networks (and use two differentRATs) at the same time. The DSDA functionality may also allow the UE 106may to simultaneously receive voice calls or data traffic on eitherphone number. In another embodiment, the UE 106 supports Dual SIM DualStandby (DSDS) functionality. The DSDS functionality may allow either ofthe two smart cards 310 in the UE 106 to be on standby waiting for avoice call and/or data connection. In DSDS, when a call/data isestablished on one SIM 310, the other SIM 310 is no longer active. Inone embodiment, DSDx functionality (either DSDA or DSDS functionality)may be implemented with a single smart card (e.g., a eUICC) thatexecutes multiple SIM applications for different carriers and/or RATs.

As noted above, the UE 106 may be configured to communicate wirelesslyusing multiple radio access technologies (RATs). As further noted above,in such instances, the cellular communication circuitry (radio(s)) 430may include radio components which are shared between multiple RATSand/or radio components which are configured exclusively for useaccording to a single RAT. Where the UE 106 comprises at least twoantennas, the antennas 435 and 436 may be configurable for implementingMIMO (multiple input multiple output) communication.

As described herein, the UE 106 may include hardware and softwarecomponents for implementing features for communicating using two or moreRATs, such as those described herein. The processor 402 of the UE device106 may be configured to implement part or all of the features describedherein, e.g., by executing program instructions stored on a memorymedium (e.g., a non-transitory computer-readable memory medium).Alternatively (or in addition), processor 402 may be configured as aprogrammable hardware element, such as an FPGA (Field Programmable GateArray), or as an ASIC (Application Specific Integrated Circuit).Alternatively (or in addition) the processor 402 of the UE device 106,in conjunction with one or more of the other components 400, 404, 406,410, 420, 430, 435, 440, 450, 460 may be configured to implement part orall of the features described herein.

FIGS. 5A and 5B—UE Transmit/Receive Logic

FIG. 5A illustrates a portion of UE 106 according to one embodiment. Asshown, UE 106 may comprise control circuitry 42 that is configured tostore and execute control code for implementing control algorithms inthe UE 106. Control circuitry 42 may include storage and processingcircuitry 28 (e.g., a microprocessor, memory circuits, etc.) and mayinclude baseband processor integrated circuit 58. Baseband processor 58may form part of wireless circuitry 34 and may include memory andprocessing circuits (i.e., baseband processor 58 may be considered toform part of the storage and processing circuitry of UE 106). Basebandprocessor 58 may comprise software and/or logic for handling variousdifferent RATs, such as GSM logic 72 and LTE logic 74, among others.

Baseband processor 58 may provide data to storage and processingcircuitry 28 (e.g., a microprocessor, nonvolatile memory, volatilememory, other control circuits, etc.) via path 48. The data on path 48may include raw and processed data associated with UE cellularcommunications and operations, such as cellular communication data,wireless (antenna) performance metrics for received signals, informationrelated to tune-away operations, information related to pagingoperations, etc. This information may be analyzed by storage andprocessing circuitry 28 and/or processor 58 and, in response, storageand processing circuitry 28 (or, if desired, baseband processor 58) mayissue control commands for controlling wireless circuitry 34. Forexample, storage and processing circuitry 28 may issue control commandson path 52 and path 50 and/or baseband processor 58 may issue commandson path 46 and path 51.

Wireless circuitry 34 may include radio-frequency transceiver circuitrysuch as radio-frequency transceiver circuitry 60 and radio-frequencyfront-end circuitry 62. Radio-frequency transceiver circuitry 60 mayinclude one or more radio-frequency transceivers. In the embodimentshown radio-frequency transceiver circuitry 60 comprises transceiver(TX) chain 59, receiver (RX) chain 61 and RX chain 63. As noted above,the two RX chains 61 and 63 may be a primary RX chain 61 and a diversityRX chain 63. The two RX chains 61 and 63 may be connected to the samelocal oscillator (LO) and thus may operate together at the samefrequency for MIMO operations. Thus the TX chain 59 and the two RXchains 61 and 63 may be considered, along with other necessarycircuitry, as a single radio. Other embodiments are of coursecontemplated. For example, the radio-frequency transceiver circuitry 60may comprise only a single TX chain and only a single RX chain, also asingle radio embodiment. Thus the term “radio” may be defined to havethe broadest scope of its ordinary and accepted meaning, and comprisesthe circuitry normally found in a radio, including either a single TXchain and a single RX chain or a single TX chain and two (or more) RXchains, e.g., connected to the same LO. The term radio may encompass thetransmit and receive chains discussed above and may also include digitalsignal processing coupled to the radio frequency circuitry (e.g., thetransmit and receive chains) associated with performing wirelesscommunication. As one example, the transmit chain may include suchcomponents as amplifier, mixer, filter, and digital analog converter.Similarly, the receive chain(s) may include, e.g., such components asamplifier, mixer, filter, and analog to digital converter. As mentionedabove, multiple receive chains may share a LO, although in otherembodiments, they may comprise their own LO. Wireless communicationcircuitry may encompass a larger set of components, e.g., including oneor more radios of the UE (transmit/receive chains and/or digital signalprocessing), baseband processors, etc. The term “cellular wirelesscommunication circuitry” includes various circuitry for performingcellular communication, e.g., as opposed to other protocols that are notcellular in nature, such as Bluetooth. Certain embodiments of theinvention described herein may operate to improve performance when asingle radio (i.e., a radio with a single TX chain and single RX chain;or a radio with a single TX chain and two RX chains, where the two RXchains are connected to the same LO) supports multiple RATs.

As shown in FIG. 5B, the radio-frequency transceiver circuitry 60 mayalso comprise two or more TX chains and two or more RX chains. Forexample, FIG. 5B shows an embodiment with a first radio 57 comprising TXchain 59 and RX chain 61 and a second radio 63 comprising a first TXchain 65 and a second TX chain 67. Embodiments are also contemplatedwhere additional TX/RX receive chains may be included in the embodimentof FIG. 5A, i.e., in addition to the one TX chain 59 and two RX chains61 and 63 shown. In these embodiments that have multiple TX and RXchains, when only one radio is currently active, e.g., the second radiois turned off to save power, certain embodiments of the inventiondescribed herein may operate to improve performance of the single activeradio when it supports multiple RATs.

Baseband processor 58 may receive digital data that is to be transmittedfrom storage and processing circuitry 28 and may use path 46 andradio-frequency transceiver circuitry 60 to transmit correspondingradio-frequency signals. Radio-frequency front end 62 may be coupledbetween radio-frequency transceiver 60 and antennas 40 and may be usedto convey the radio-frequency signals that are produced byradio-frequency transceiver circuitry 60 to antennas 40. Radio-frequencyfront end 62 may include radio-frequency switches, impedance matchingcircuits, filters, and other circuitry for forming an interface betweenantennas 40 and radio-frequency transceiver 60.

Incoming radio-frequency signals that are received by antennas 40 may beprovided to baseband processor 58 via radio-frequency front end 62,paths such as paths 54 and 56, receiver circuitry in radio-frequencytransceiver 60, and paths such as path 46. Path 54 may, for example, beused in handling signals associated with transceiver 57, whereas path 56may be used in handling signals associated with transceiver 63. Basebandprocessor 58 may convert received signals into digital data that isprovided to storage and processing circuitry 28. Baseband processor 58may also extract information from received signals that is indicative ofsignal quality for the channel to which the transceiver is currentlytuned. For example, baseband processor 58 and/or other circuitry incontrol circuitry 42 may analyze received signals to produce variousmeasurements, such as bit error rate measurements, measurements on theamount of power associated with incoming wireless signals, strengthindicator (RSSI) information, received signal code power (RSCP)information, reference symbol received power (RSRP) information,signal-to-interference ratio (SINR) information, signal-to-noise ratio(SNR) information, channel quality measurements based on signal qualitydata such as Ec/Io or Ec/No data, etc.

Radio-frequency front end 62 may include switching circuitry. Theswitching circuitry may be configured by control signals received fromcontrol circuitry 42 (e.g., control signals from storage and processingcircuitry 28 via path 50 and/or control signals from baseband processor58 via path 51). The switching circuitry may include a switch (switchcircuit) that is used to connect TX and RX chain(s) to antennas 40A and40B. Radio-frequency transceiver circuitry 60 may be configured bycontrol signals received from storage and processing circuitry over path52 and/or control signals received from baseband processor 58 over path46.

The number of antennas that are used may depend on the operating modefor UE 106. For example, as shown in FIG. 5A, in normal LTE operations,antennas 40A and 40B may be used with respective receivers 61 and 63 toimplement a receive diversity scheme, such as for MIMO operations. Withthis type of arrangement, two LTE data streams may be simultaneouslyreceived and processed using baseband processor 58. When it is desiredto monitor a GSM paging channel for incoming GSM pages, one or both ofthe antennas may be temporarily used in receiving GSM paging channelsignals.

Control circuitry 42 may be used to execute software for handling morethan one radio access technology. For example, baseband processor 58 mayinclude memory and control circuitry for implementing multiple protocolstacks such as a GSM protocol stack 72 and an LTE protocol stack 74.Thus, protocol stack 72 may be associated with a first radio accesstechnology such as GSM (as an example), and protocol stack 74 may beassociated with a second radio access technology such as LTE (as anexample). During operation, UE 106 may use GSM protocol stack 72 tohandle GSM functions and may use LTE protocol stack 74 to handle LTEfunctions. Additional protocol stacks, additional transceivers,additional antennas 40, and other additional hardware and/or softwaremay be used in UE 106 if desired. The arrangement of FIGS. 5A and 5B ismerely illustrative. In one embodiment, one or both of the protocolstacks may be configured to implement the methods described in theflowcharts below.

In one embodiment of FIG. 5A (or 5B), the cost and complexity of UE 106may be minimized by implementing the wireless circuitry of FIG. 5A (or5B) using an arrangement in which baseband processor 58 andradio-transceiver circuitry 60 are used to support both LTE and GSMtraffic.

The GSM radio access technology may generally be used to carry voicetraffic, whereas the LTE radio access technology may generally be usedto carry data traffic. To ensure that GSM voice calls are notinterrupted due to LTE data traffic, GSM operations may take priorityover LTE operations. To ensure that operations such as monitoring a GSMpaging channel for incoming paging signals do not unnecessarily disruptLTE operations, control circuitry 42 can, whenever possible, configurethe wireless circuitry of UE 106 so that wireless resources are sharedbetween LTE and GSM functions.

When a user has an incoming GSM call, the GSM network may send UE 106 apaging signal (sometimes referred to as a page) on the GSM pagingchannel using base station 102. When UE 106 detects an incoming page, UE106 can take suitable actions (e.g., call establishment procedures) toset up and receive the incoming GSM call. Pages are typically sentseveral times at fixed intervals by the network, so that devices such asUE 106 will have multiple opportunities to successfully receive a page.

Proper GSM page reception may require that the wireless circuitry of UE106 be periodically tuned to the GSM paging channel, referred to as atune-away operation. If the transceiver circuitry 60 fails to tune tothe GSM paging channel or if the GSM protocol stack 72 in basebandprocessor 58 fails to monitor the paging channel for incoming pages, GSMpages will be missed. On the other hand, excessive monitoring of the GSMpaging channel may have an adverse impact on an active LTE data session.Embodiments of the invention may comprise improved methods for handlingtune-away operations, as described below.

In some embodiments, in order for the UE 106 to conserve power, the GSMand LTE protocol stacks 72 and 74 may support idle mode operations.Also, one or both of the protocol stacks 72 and 74 may support adiscontinuous reception (DRX) mode and/or a connected discontinuousreception (CDRX) mode. DRX mode refers to a mode which powers down atleast a portion of UE circuitry when there is no data (or voice) to bereceived. In DRX and CRDX modes, the UE 106 synchronizes with the basestation 102 and wakes up at specified times or intervals to listen tothe network. DRX is present in several wireless standards such as UMTS,LTE (Long-term evolution), WiMAX, etc. The terms “idle mode”, “DRX” and“CDRX” are explicitly intended to at least include the full extent oftheir ordinary meaning, and are intended to encompass similar types ofmodes in future standards.

Selective Measurement and/or Synchronization Based on Current ChannelConditions

As discussed above, a UE may use a single radio to communicate using twodifferent RATs. For example, the UE may use a single radio tocommunicate using a first RAT and may periodically tune away in order toperform various actions for a second RAT, such as page decoding. In thisexample, the UE may be considered as maintaining a connection to bothRATs using the same radio, even though it may only communicate using oneRAT at a time. In one embodiment, the first RAT may be LTE and thesecond RAT may be GSM, although other combinations of RATs areenvisioned. In some cases, it may be typical to tune away periodically(e.g., at each DRX cycle) in order to perform page decoding for thesecond RAT. In addition, while tuned away to perform page decoding, theUE may also perform neighbor cell measurement and/or synchronization forthe second RAT.

However, while page decoding may be performed in a relatively smalleramount of time (e.g., a few milliseconds), neighbor cell measurementand/or synchronization may take a significantly longer amount of time(e.g., 50-100 milliseconds). As a result, if the UE performs pagedecoding, neighbor cell measurement, and synchronization at each tuneaway to the second RAT, performance of the first RAT may besignificantly affected. For example, if the UE tunes away from the firstRAT for a significant period of time (e.g., greater than 40 or 50milliseconds), the first RAT may consider the UE to be experiencing adeep fading scenario since the UE does not communicate on the first RATduring this significant period of time. As a result, the first RAT mayreduce the modulation and coding or resource blocks assigned to the UEfor the first RAT, which may reduce throughput for the UE when it usesthe first RAT, e.g., after tuning back to the first RAT, which isundesirable.

Accordingly, instead of consistently performing cell measurement and/orsynchronization for the second RAT, e.g., each DRX cycle of the secondRAT, the UE may selectively perform cell measurement and/orsynchronization, e.g., based on current conditions of the second RAT.For example, if the current channel conditions for the currentlyselected base station on the second RAT is sufficient (e.g., if thereceived signal strength indication (RSSI) of the current base stationon the second RAT exceeds a threshold, e.g., of −80 dBm), then the UEmay not perform measurement and/or synchronization, and may simplyperform page decoding. For example, while the channel conditions exceedthe threshold, the UE may only perform page decoding each cycle (e.g.,each DRX cycle) and may not perform neighbor cell measurement orsynchronization. Alternatively, or additionally, the UE may perform pagedecoding and measurement and not perform synchronization (e.g., in caseswhere synchronization is the activity that causes the tune away toexceed 30-50 milliseconds). In further embodiments, the UE may performpage decoding and synchronization, but not measurement (e.g., in caseswhere measurement is the activity that causes the tune away to exceed30-50 milliseconds). However, where the current channel conditions ofthe current base station of the second RAT do not exceed the threshold,the UE may be configured to perform page decoding as well as neighbormeasurement and/or synchronization, e.g., in order to ensure adequateperformance for the second RAT.

By dynamically determining whether to perform neighbor base stationmeasurement and/or synchronization for the second RAT, throughput of thefirst RAT may be improved. For example, this process may reduce tuneaways from having 20% that exceed 30 milliseconds, to only 2% exceeding30 milliseconds, which may result in a throughput gain for the first RATof 20%. Additionally, this process may conserve battery power byreducing the required number of neighbor base station measurementsand/or synchronizations.

FIG. 6—Selectively Performing Measurement and/or Synchronization

FIG. 6 is a flowchart diagram illustrating a method for selectivelyperforming neighbor base station measurement and/or synchronization by aUE device (such as UE 106) that uses a first radio for both a first RATand a second RAT (e.g., LTE and GSM, although other combinations of RATsare envisioned). The method shown in FIG. 6 may be used in conjunctionwith any of the systems or devices shown in the above Figures, amongother devices. In various embodiments, some of the method elements shownmay be performed concurrently, in a different order than shown, or maybe omitted. Note also that additional method elements may also beperformed as desired. The method may be performed as follows.

As shown, in 602, the UE may communicate using the first radio using thefirst RAT. In one embodiment, the first RAT may be LTE, although otherRATs are envisioned.

In 604, the UE may compare a current channel condition of a current basestation of the second RAT to a threshold. The current channel conditionmay be a stored channel condition, e.g., from a closest previousmeasurement of the channel condition, or the current channel conditionmay be measured in order to compare the current channel condition to thethreshold, e.g., during or prior to each cycle (e.g., each DRX cycle).In one embodiment, the current channel condition may be an RSSI,although other measurements of channel conditions (or combinationsthereof) are envisioned, such as RSCP, RSRP, SINR, SNR, and/or otherpossibilities. The threshold may be specific to determining whether toperform neighbor base station measurement and/or synchronization for thesecond RAT. Alternatively, the threshold may be a general threshold thatthe UE may also use for the purpose of determining whether to performneighbor base station measurement and/or synchronization, as desired.

In 606, if the current channel condition of the second RAT exceeds thethreshold, the UE may use the first radio to perform page decoding usingthe second RAT. In other words, the UE tune the first radio away fromthe first RAT to the second RAT in order to perform page decoding on thesecond RAT. However, since the current channel condition of the secondRAT exceeds the threshold, the UE may not perform neighbor base stationmeasurement and/or synchronization at 606. For example, the UE may onlyperform page decoding and may not perform neighbor base stationmeasurement or neighbor base station synchronization. Alternatively,e.g., where measurement would not increase the tune away time to asignificant period of time (e.g., greater than 30-50 milliseconds), theUE may perform page decoding and measurement, but may not performsynchronization. Further, e.g., where synchronization would not increasethe tune away time to a significant period of time, the UE may performpage decoding and synchronization, but may not perform measurement. Inone embodiment performing the page decoding in 606 may be performed atthe current DRX cycle. In addition, while the measurement and/orsynchronization is discussed as occurring at or near a page decoding, itmay instead or also be performed at other times, based on the threshold,as desired.

In 608, if the current channel condition of the second RAT does notexceed the threshold, the UE may use the first radio to perform pagedecoding as well as neighbor base station measurement and/orsynchronization using the second RAT. For example, the UE may performpage decoding for the second RAT, measurement of neighboring basestations of the second RAT, and synchronization to one or moreneighboring base stations of the second RAT.

The combination of neighbor cell measurement and neighbor cellsynchronization may be referred to as “neighbor cell detection”.Additionally, the use of the threshold in 606 and 608 may more generallyapply to neighbor cell detection, e.g., the neighbor cell detection maybe skipped if the current channel condition exceeds the threshold, butmay be performed if the current channel condition falls below thethreshold.

After 606 or 608 (depending on the case), the method may return to 602,where the UE may tune back to the first RAT to continue communicationsusing the first RAT. The method of FIG. 6 may be performed in a periodicfashion, e.g., at each DRX cycle. Alternatively, the comparison of thecurrent channel conditions to the threshold may not be performed eachcycle, but the result of the comparison may be used in each cycle untila new comparison is performed. For example, a new comparison may be madeeach time the current channel condition is measured, and then applied tosubsequent cycles.

Tune Away During Handover

As discussed above, a UE may use a single radio to communicate using twodifferent RATs. For example, the UE may use a single radio tocommunicate using a first RAT and may periodically tune away in order toperform various actions for a second RAT, such as page decoding. In thisexample, the UE may be considered as maintaining a connection to bothRATs using the same radio, even though it may only communicate using oneRAT at a time. In one embodiment, the first RAT may be LTE and thesecond RAT may be GSM, although other combinations of RATs areenvisioned. In some cases, it may be typical to tune away periodically(e.g., at each DRX cycle) in order to perform page decoding for thesecond RAT. In addition, while tuned away to perform page decoding, theUE may also perform neighbor cell measurement and/or synchronization.

When the UE is at the edge of a current cell in the first RAT, it isalso possible that the UE may be at the edge of a current cell for thesecond RAT. As a result, the UE may have a conflict between performinghandover in the first RAT (and/or associated actions) and performinghandover in the second RAT (and/or associated actions). In some cases,the second RAT may have a higher priority than the first RAT (e.g.,because of the need for performing page decoding for an incoming voicecall), which may interrupt the first RAT handover process. Accordingly,if the second RAT tune away interrupts the first RAT handover process,the first RAT handover process may fail. In particular, UE may tune awayfrom the first RAT to the second RAT to perform page decoding as well assecond RAT measurement, synchronization, and/or handover procedures(e.g., for neighbor cell SCH or FCCH), which may result in a significanttune away period that may cause issues for the first RAT handover.

Accordingly, if the first RAT is in a handover process (e.g., is in arandom access channel (RACH) state), tune away requests for performingcertain processes (e.g., measurement, synchronization, SCH processes,FCCH processes, etc., e.g., which may be associated with handoverprocesses) for the second RAT may be blocked. However, in oneembodiment, page decoding processes for the second RAT may not beblocked during this handover process. Thus, similar to embodimentsabove, the UE may perform page decoding on tune away to the second RATbut may not perform measurement and/or synchronization for the secondRAT in order to avoid a long tune away time that could affect the firstRAT handover process. Additionally, in some embodiments, the requestsfor performing the non-paging related processes for the second RAT maybe delayed until after the first RAT completes the handover processand/or exits the RACH state. Accordingly, the UE may be better able tocomplete the handover process for the first RAT and may continue toperform page decoding for the second RAT.

FIG. 7—Page Decoding During Handover

FIG. 7 is a flowchart diagram illustrating a method for performing pagedecoding by a UE device (such as UE 106) that uses a first radio forboth a first RAT and a second RAT (e.g., LTE and GSM, although othercombinations of RATs are envisioned). The method shown in FIG. 7 may beused in conjunction with any of the systems or devices shown in theabove Figures, among other devices. In various embodiments, some of themethod elements shown may be performed concurrently, in a differentorder than shown, or may be omitted. Note also that additional methodelements may also be performed as desired. The method may be performedas follows.

As shown, in 702, e.g., while on a cell edge of a first base station ofa first RAT, the UE may begin a handover process for the first RAT usingthe first radio. For example, the UE may enter a handover process of thefirst RAT in response to measurements of signal strengths of basestations of the first RAT, a message from the first RAT network, and/orany of a variety of reasons. In one embodiment, the first RAT may beLTE, although other RATs are envisioned.

In 704, during the handover process, the UE may tune away from the firstRAT to perform page decoding using the second RAT, e.g., in response toa page decode request from the second RAT (e.g., a stack associated withthe second RAT). In one embodiment, the UE may perform the page decodingfor the second RAT during a RACH state of the first RAT. Similar todiscussions above, the UE may not perform measurement of neighboringbase stations, synchronization to neighboring base stations, SCH or FCCHprocesses, and/or generally any handover processes associated with thesecond RAT, in addition to the page decoding. As a result, the UE maynot tune away from the first RAT to the second RAT for a significantperiod of time (e.g., greater than 30-50 milliseconds) that would causeissues for the handover process of the first RAT. In one embodiment,these processes may be simply delayed until after the handover processof the first RAT is completed, e.g., at the next DRX cycle aftercompletion of the handover.

In some embodiments, 704 may include blocking any received requests toperform the discussed processes (e.g., the measurement, synchronization,SCH or FCCH processes, handover processes, etc. of the second RAT).However, in one embodiment, similar to discussions above, one or more ofthese processes may not be blocked if they do not cause a significantdelays in returning to the first RAT, e.g., measurement may be performedbut not synchronization if measurement is sufficiently short. In otherembodiments, however, all of these processes may be blocked duringhandover of the first RAT. The time required to perform the handoverprocess may be referred to as a “handover period”. Thus, during suchhandover periods, the UE may not perform one or more of the identifiedprocesses of the second RAT, e.g., but may still perform page decoding,as desired.

In 706, the UE may complete the first handover process for the firstRAT.

In 708, after the handover period, the UE may perform the blockedprocesses for the second RAT, e.g., during a next cycle, such as a nextDRX cycle of the second RAT. For example, the UE may perform pagedecoding as well as any requested or desired measurement,synchronization, SCH or FCCH processes, and/or handover procedures forthe second RAT. Alternatively, or additionally, these delayed processesmay begin sooner than the next cycle, e.g., once the first handoverprocess for the first RAT is completed.

Thus, for example, where the first RAT and the second RAT are bothattempting to perform handover (or said another way, when handover isrequired for both of the first RAT and the second RAT), the UE maycomplete the handover process for the first RAT, followed by performingthe handover process for the second RAT.

FIG. 8 Exemplary Timing Diagram

FIG. 8 is an exemplary timing diagram that corresponds to one embodimentof the method of FIG. 7. In particular, as shown, a handover processassociated with the first RAT 800 may initially begin. This handoverprocess includes a RACH state (e.g., approximately 50 milliseconds)followed by an RRC state (e.g., approximately 50-100 milliseconds).During the RACH state, the UE may tune away from the first RAT to thesecond RAT to perform page decoding (e.g., for 10 milliseconds), e.g.,based on a DRX cycle of the second RAT. After the handover process ofthe first RAT finishes, the UE may perform measurement, synchronization,and/or handover processes for the second RAT as shown at 850, which maytake approximately 100 milliseconds.

Embodiments of the present invention may be realized in any of variousforms. For example, in some embodiments, the present invention may berealized as a computer-implemented method, a computer-readable memorymedium, or a computer system. In other embodiments, the presentinvention may be realized using one or more custom-designed hardwaredevices such as ASICs. In other embodiments, the present invention maybe realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE) may be configured to includea processor (or a set of processors) and a memory medium, where thememory medium stores program instructions, where the processor isconfigured to read and execute the program instructions from the memorymedium, where the program instructions are executable to implement anyof the various method embodiments described herein (or, any combinationof the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of suchsubsets). The device may be realized in any of various forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A method, comprising: at a user equipment device(UE) comprising a first radio, wherein the first radio is configurableto operate according to a first radio access technology (RAT) and asecond RAT: communicating, using the first radio of the UE, using thefirst RAT; performing, using the first radio of the UE, a measurement ofcurrent channel condition of the second RAT; determining if the currentchannel condition is less than a threshold; performing, using the firstradio of the UE, a neighbor cell synchronization for the second RAT ifthe current channel condition of the second RAT is less than thethreshold, wherein a neighbor cell synchronization is not performed ifthe current channel condition of the second RAT is not less than thethreshold; performing, using the first radio of the UE, a page decodeevery discontinuous receive (DRX) cycle of the second RAT;communicating, using the first radio of the UE, using the first RAT,after said performing neighbor cell synchronization and the page decodeevery DRX cycle of the second RAT, wherein during said performing theneighbor cell synchronization and performing the page code, the UEmaintains a connection using the first RAT.
 2. The method of claim 1,further comprising: performing, by the first radio of the UE, a neighborcell measurement of the second RAT if the current channel condition ofthe second RAT is less than the threshold, wherein a neighbor cellmeasurement is not performed if the current channel condition of thesecond RAT is not less than the threshold.
 3. The method of claim 1,wherein said performing neighbor cell synchronization is comprisedwithin performing neighbor cell detection, wherein said performing theneighbor cell detection comprises performing neighbor cell measurement,and wherein the neighbor cell detection is not performed if the currentchannel condition of the second RAT is not less than the threshold. 4.The method of claim 1, wherein the UE comprises only a single radio forperforming cellular communication, wherein the single radio is the firstradio.
 5. The method of claim 1, wherein the UE comprises two smartcards which are each configured to implement SIM (Subscriber IdentityModule) functionality, wherein the UE is configured to implement DSDA(Dual SIM Dual Active) functionality using the first radio.
 6. Themethod of claim 1, wherein the threshold is approximately −80 dBm. 7.The method of claim 1, wherein said determining if the current channelquality is less than the threshold is performed every DRX cycle of thesecond RAT.
 8. The method of claim 1, wherein said performing theneighbor cell synchronization is performed every DRX cycle of the secondRAT.
 9. The method of claim 1, wherein said performing a measurement ofcurrent channel condition comprises measuring a received signal strengthof the second RAT, wherein performing the neighbor cell synchronizationis performed if the current channel condition is less than thethreshold.
 10. The method of claim 1, wherein the first RAT compriseslong term evolution (LTE).
 11. A user equipment device (UE) configuredto perform selective neighbor cell measurement, comprising: a firstradio, wherein the first radio is configured to perform communicationusing a first radio access technology (RAT) and a second RAT andmaintain a connection to both the first RAT and the second RATconcurrently; and one or more processors coupled to the first radio,wherein the one or more processors and the first radio are configuredto: perform a measurement of received signal strength of the second RAT;perform a page decode every discontinuous receive (DRX) cycle of thesecond RAT; determine if the received signal strength is less than athreshold; perform a neighbor cell measurement of the second RAT inconjunction with the page decode if the received signal strength of thesecond RAT is less than the threshold, wherein a neighbor cellmeasurement is not performed if the received signal strength of thesecond RAT is not less than the threshold; communicate using the firstRAT after performing the page decode and the neighbor cell measurementof the second RAT.
 12. The UE of claim 11, wherein the one or moreprocessors and the first radio are configured to perform a neighbor cellsynchronization of the second RAT in conjunction with the page decodeand the neighbor cell measurement if the received signal strength of thesecond RAT is less than the threshold.
 13. The UE of claim 11, whereinthe UE comprises only a single radio for performing cellularcommunication, wherein the single radio is the first radio.
 14. The UEof claim 11, wherein said determining if the received signal strength isbelow the threshold and said performing the neighbor cell measurement ifthe received signal strength is less than the threshold is performedevery DRX cycle of the second RAT.
 15. The UE of claim 11, wherein thethreshold is approximately −80 dBm.
 16. The UE of claim 11, wherein thefirst RAT comprises long term evolution (LTE) and wherein the second RATcomprises global system for mobile communications (GSM).
 17. The UE ofclaim 11, wherein the UE comprises two smart cards which are eachconfigured to implement SIM (Subscriber Identity Module) functionality,wherein the UE is configured to implement DSDA (Dual SIM Dual Active)functionality using the first radio.
 18. A non-transitory, computeraccessible memory medium storing program instructions for performingselective measurement by a user equipment device (UE), wherein the UEcomprises only a single radio for communicating using a first radioaccess technology (RAT) and a second RAT, wherein the programinstructions are executable by a processor to: communicate, by thesingle radio of the UE, using the first RAT; perform, by the singleradio of the UE, a measurement of a current channel condition of thesecond RAT; determine if the current channel condition of the second RATis less than a threshold; and perform, by the single radio of the UE, aneighbor cell detection of the second RAT if the current channelcondition of the second RAT is less than the threshold, wherein aneighbor cell detection is not performed if the current channelcondition of the second RAT is not less than the threshold, whereinduring performing the neighbor cell detection, the UE maintains aconnection using the first RAT.
 19. The non-transitory, computeraccessible memory medium of claim 18, wherein said performing theneighbor cell detection if the current channel condition of the secondRAT is less than the threshold is performed each discontinuous reception(DRX) cycle of the second RAT.
 20. The non-transitory, computeraccessible memory medium of claim 18, wherein the UE comprises two smartcards which are each configured to implement SIM (Subscriber IdentityModule) functionality, wherein the UE implements DSDA (Dual SIM DualActive) functionality using the single radio.